HitTestResultCallback Delegate

Definition

public delegate System::Windows::Media::HitTestResultBehavior HitTestResultCallback(HitTestResult ^ result);

public delegate System.Windows.Media.HitTestResultBehavior HitTestResultCallback(HitTestResult result);

type HitTestResultCallback = delegate of HitTestResult -> HitTestResultBehavior

Public Delegate Function HitTestResultCallback(result As HitTestResult) As HitTestResultBehavior 

Parameters

Return Value

A HitTestFilterBehavior that represents the action resulting from the hit test.

Examples

The following example shows how to invoke HitTest by using a HitTestResultCallback value. The corresponding hit test callback method is also defined.

// Capture the mouse event and hit test the coordinate point value against
// the child visual objects.
void MyVisualHost_MouseLeftButtonUp(object sender, System.Windows.Input.MouseButtonEventArgs e)
{
 // Retrieve the coordinates of the mouse button event.
 System.Windows.Point pt = e.GetPosition((UIElement)sender);

 // Initiate the hit test by setting up a hit test result callback method.
 VisualTreeHelper.HitTest(this, null, new HitTestResultCallback(myCallback), new PointHitTestParameters(pt));
}

// If a child visual object is hit, toggle its opacity to visually indicate a hit.
public HitTestResultBehavior myCallback(HitTestResult result)
{
 if (result.VisualHit.GetType() == typeof(DrawingVisual))
 {
 if (((DrawingVisual)result.VisualHit).Opacity == 1.0)
 {
 ((DrawingVisual)result.VisualHit).Opacity = 0.4;
 }
 else
 {
 ((DrawingVisual)result.VisualHit).Opacity = 1.0;
 }
 }

 // Stop the hit test enumeration of objects in the visual tree.
 return HitTestResultBehavior.Stop;
}

' Capture the mouse event and hit test the coordinate point value against
' the child visual objects.
Private Sub MyVisualHost_MouseLeftButtonUp(ByVal sender As Object, ByVal e As MouseButtonEventArgs)
 ' Retrieve the coordinates of the mouse button event.
 Dim pt As Point = e.GetPosition(CType(sender, UIElement))

 ' Initiate the hit test by setting up a hit test result callback method.
 VisualTreeHelper.HitTest(Me, Nothing, New HitTestResultCallback(AddressOf myCallback), New PointHitTestParameters(pt))
End Sub

' If a child visual object is hit, toggle its opacity to visually indicate a hit.
Public Function myCallback(ByVal result As HitTestResult) As HitTestResultBehavior
 If result.VisualHit.GetType() Is GetType(DrawingVisual) Then
 If (CType(result.VisualHit, DrawingVisual)).Opacity = 1.0 Then
 CType(result.VisualHit, DrawingVisual).Opacity = 0.4
 Else
 CType(result.VisualHit, DrawingVisual).Opacity = 1.0
 End If
 End If

 ' Stop the hit test enumeration of objects in the visual tree.
 Return HitTestResultBehavior.Stop
End Function

Remarks

The hit test callback method defines the actions that you perform when a hit test is identified on a particular visual object in the visual tree. After you perform the actions, your callback is expected to return a HitTestResultBehavior value that determines whether to continue iterating through the visual tree for any other visual objects.